Need advice on hosting and IP black lists

Hi guys,
I'm interested in what is the best practices to protect Zimbra's server public IP to become blacklisted if one or some of the hosted email clients would start to send mass ads/spam emails.
I think about dedicating 2-3 public IP addresses to Zimbra host and change it if one become blacklisted. But it is slow solution, it takes long time while DNS records updates on the internet.
Also I think about DNS round robin solution whith 3 A host records with different IP addresses, and all RDNS records of these IP addresses resolves to the same DNS name. Is it good solution?
What other possibilities?